Chromosome Behavior in the Pollen Mother Cells of “<i>Shogoin-daikon</i>”and“<i>Nerima-daikon</i>, ”the Horticultural Varieties of <i>Raphanus sativus</i>, L

Abstract

Chromosome behavior in the pollen mother cells of two horticultural varieties of Raphanus sativus, L.“Shogoin-daikon”and“Nerima-daikon, ” was examined.1. In the diakinesis nucleus, a tetravalent or a hexavalent chromosome is often found besides the ordinary bivalent chromosomes. These polyvalent chromosomes consist of four or six univalent chromosomes attached end-to-end successively in the form of a chain (Figs. 1, 2). A ring was not found.2. Frequency of occurrence of nuclei at diakinesis with polyvalent chromosome was examined in“Shogoin-daikon”and“Nerima-daikon”. The results are given in Table 1.3. In“Shogoin-daikon, ” the number of interstitial and terminal chiasmata in chromosomes was counted in mid- and late diakinesis nuclei in which no polyvalent chromosome was found, The results are given in Table 2 A, B.4. At the beginning of metaphase, the tetravalent chromosome is resolved into two bivalent chromosomes and the hexavalent chromosome into three bivalent chromosomes. The polyvalent chromosomes are found very rarely in the metaphase equatorial plate (Fig. 4). From metaphase onward, all chromosomes are found to behave themselves after the ordinary manner.5. The chiasmata in metaphase chromosomes are all terminal and no interstitial ones are found. Table 2 shows the number of chromosomes with one and two chiasmata counted in ten cells of“Shogoin-daikon”at metaphase.